http_charset.rb

class HttpCharset
  def initialize(content_type)
    @content_type = content_type
  end
  def encoding
    return nil unless @content_type
    par = @content_type.split(';').select do |c|
      c.split('=').first.strip == 'charset'
    end.first
    return nil unless par
    par.split('=').last.strip
  end
  def encode(str,to)
    atual = encoding
    return str unless atual
    str.force_encoding(atual).encode(to)
  end
end

http_response_utf8.rb

require 'http_charset'
  
class Net::HTTPResponse
  alias :super_body :body
  def body
    HttpCharset.new(self['content-type']).encode(super_body,'UTF-8')
  end 
end